qapi/machine: Clean up documentation around CpuInstanceProperties

CpuInstanceProperties' doc comment describes its members as properties
to be passed to device_add when hot-plugging a CPU.

This was in fact the initial use of this type, with
query-hotpluggable-cpus: letting management applications find out what
properties need to be passed with device_add to hot-plug a CPU.

We've since added other uses: set-numa-node (commit 419fcdec3c1 and
f3be67812c2), and query-cpus-fast (commit ce74ee3dea6).  These are not
about device-add.

query-hotpluggable-cpus uses CpuInstanceProperties within
HotpluggableCPU.  Lift the documentation related to device-add from
CpuInstanceProperties to HotpluggableCPU.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-ID: <20240711112228.2140606-3-armbru@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: John Snow <jsnow@redhat.com>
diff --git a/qapi/machine.json b/qapi/machine.json
index f15ad1b..50ff102 100644
--- a/qapi/machine.json
+++ b/qapi/machine.json
@@ -960,9 +960,7 @@
 ##
 # @CpuInstanceProperties:
 #
-# List of properties to be used for hotplugging a CPU instance, it
-# should be passed by management with device_add command when a CPU is
-# being hotplugged.
+# Properties identifying a CPU.
 #
 # Which members are optional and which mandatory depends on the
 # architecture and board.
@@ -996,9 +994,6 @@
 #
 # @thread-id: thread number within the core the CPU  belongs to
 #
-# .. note:: Management should be prepared to pass through additional
-#    properties with device_add.
-#
 # Since: 2.7
 ##
 { 'struct': 'CpuInstanceProperties',
@@ -1020,7 +1015,8 @@
 #
 # @type: CPU object type for usage with device_add command
 #
-# @props: list of properties to be used for hotplugging CPU
+# @props: list of properties to pass for hotplugging a CPU with
+#     device_add
 #
 # @vcpus-count: number of logical VCPU threads @HotpluggableCPU
 #     provides
@@ -1028,6 +1024,9 @@
 # @qom-path: link to existing CPU object if CPU is present or omitted
 #     if CPU is not present.
 #
+# .. note:: Management should be prepared to pass through additional
+#    properties with device_add.
+#
 # Since: 2.7
 ##
 { 'struct': 'HotpluggableCPU',